Telephone system



m. w u m 5 Sheets-Sheet l J. WICKS TELEPHONE SYSTEM Nov. 6, 1951 Original Filed March 29, 1947 John Wicks A'rys.

J. VVICKS TELEPHONE SYSTEM Nov. 6, 1951 3 Sheets-Sheet 2 Original Filed March 29, 1947 s .182 n N32 mm om 52:. SEOI.- mm mm2-.r v w m w mhm fmm w W .M En ON 19m im m :,255 om ammmmlln- 5ML LM A www .NS 78m w #km E mz. 3 om@ @z zotw www@ 1 .oroz @WM m fll. S j ma mi: www rf ijn m8 Jv Us YITNNmm .v mo T5 F 5% mi: mm Nw@ mmm www c LN. E \1\A-m 8m .ma 5m S mmm 55E mz3 w nl' t 5m. 4 #55 mi@ www v2 S ,i Y K w m mm mmm mm mo o mw JNE Nov. 6, 1951 J. wlcKs TELEPHONE SYSTEM 5 Sheets-Sheet 5 Original Filed March 29, 1947 CNN INVENTOR. John Wicks NNN mmm

15N murio Ezmo Patented Nov. 6, 1951 John Wicks, Biloxi, Miss assigner to Automatic Electric Laboratories, Inc.,'Chicago, Ill., a cor:

poration of Delaware Original application March 29, 1947, Serial No. i

738,116. Divided and this applicati@ June `e1., 1949, Serial No. 100,400

The present invention relates to automatic telephone systems and more particularly to such systems in which different groups of subscriber substations are rendered corresponding diierent classes of service. This application is a division of the copending application of John Wicks, Serial No. 738,116, filed March 29, 1947, now Patent No. 2,518,210 dated August 8, 1950.

In an automatic telephone system serving a central oflce area and the adjacent suburban areas, calls from the subscriber substations in the central oice area that are to be completed to subscriber substationsin the suburban areas are usually first yextended to an operator switchboard in the central oce area and then routed by the operators thereat to the' subscriber substations in the suburban areas. While this system is entirely satisfactory in operation, a large switchboard in the central oice, staffed by a great number of operators, is required in order to complete the calls from the central oflice area to the suburban areas.

Accordingly, it is an object of the present invention to p rovide an automatic telephone system comprising an improved switching arrangement; whereby usubscriber substations arranged in a first group in the central oice are rendered a iirst class of service permitting them to set up connections for any desired time interval to subscriber substations inthe suburban areas; subscriber substations arranged in a second group in the central office are rendered a second class of service permitting them to set up connections for a limited time interval to subscriber substations in the suburban areas; and subscriber substations arranged in a third group in the central office are `rendered a third class of service preventing them from setting up connections to subscriber substations in the suburban areas.

Another object of the invention is kto provide an automatic telephone system in which different classes of service are rendered to the subscriber substations; wherein the classes of service are selectively established `by an improved varrangement including different types of digit 'transmitting mechanism disposed at the subscriber substations.

Another object of the invention is to provide an automatic telephone -system in which different classes of service are rendered to subscriber substations; wherein the class of service rendered to a given calling subscriber substation is determined by a unique control transmitted by the digit -transmitting mechanism incident to a standard operation thereof. f' v claims. (c1. rief-27) A further object of theinvention is tprprgvide an automatic telephone system of thetype noted that comprises improved switching 7apparat A which is selectively responsive to the unigne een-v trols transmitted .from thediierent classes or subscriber sub'stations in order to ,render the rcorresponding classes 4of service. v

Further features ofthe invention partain to the particular arrangement of the ,circuit @Les ments Vof the system', wherebythe above-,outlined and additional operating features thereof are a, tained. A

rl'he invention, both as to its organization and method 0f operation, Ytogether With further 0bjects and advantages thereof, will best be understood by reference to the following speciiication taken in connection kwith .thel accompanying drawings in whichFigures 1 to 3, inclusive, taken together, illustrate the details of an automatic telephone system having incorporated therein the feature of the present invention. More' particu-J larly, Fiss. 1 and `2 ,Should b arranged ,f'm 'left to` right in end-toflend relation; andFig. 3 should be arrangedlongitudinally/below Fig. 2.

Referring now-more particularly to Figs. 1 Vto 3, inclusive, ofthe drawings, vthere is illustrated an automatic telephone system comprising a central o iiice l0, a distant exchange 2G anda remote ex# change 30. The central oiiice l0 is connected to the distant exchange 2li by a group of tenV trunk lines, including the trunk line 395i; and the central oice :la is connected to the remote `exchange 30 by a ,group of fourteen trunk lines, including the trunk line 286.

The central oiice lil may serve a group of several hundred subscriber substations rendered three individual classes of service, including'nonrestricted service, limited service and restricted service. A frst group of subscriber substations, including the subscriber substation T`l2,`is rendered Inonrestricted service;l a ksecond vgroup of subscriber substations, including the'su'bscriber substation TH, rendered limited serv-ice; and e third ,graue 9i Subscriber ,sesteiios .iridlud'g the Subscriber substaiqn Till, 11S reudred- Stricied .Service- .Eefrh Subrber substatiorfi provided vithsubsietion apparatus and is con# nected by an associated subscriber lineto a line switch individual thereto. The subscriber y,substation 'Il- 2 is connected bythe 4associated sub.- scriber line Il to the line switch i8 individual thereto; the subscriber `substation TII is connected by the associated subscriber line t5 tothe line switch ylli individual thereto;` and Athe subscriber substation lTil) is connected Iby the associ:

ated subscriber line I3 to the line switch I4 individual thereto. Each of the subscriber substations rendered non-restricted service and each of the subscriber substations rendered limited service is provided with a meter individual thereto which is connected to the associated line switch. The meter MI| is individual to the subscriber substation TII and is connected to the individually associated line switch I6; while the meter MI 2 is individual to the subscriber substation TI 2 and is connected to the individually associated line switch I8. Each subscriber substation rendered non-restricted service, such, for example, as the subscriber substation TI2, also comprises a dial having ten ordinary digit finger holes therein and an eleventh digit nger hole which may be utilized in order to cause the dial to transmit a series of twelve impulses in a continuous group and constituting the digit Y; each subscriber substation rendered limited service, such, for example, as the subscriber substation TI I, also comprises a dial having ten ordinary digit nger holes therein and an eleventh digit ringer hole which may be utilized in order to cause the dial to transmit a series of eleven impulses in a continuous group and constituting the digit X; and each subscriber substation rendered restricted service, such, for example, as the subscriber substation TIO, also comprises a dial of conventional construction having ten ordinary digit finger holes therein.

Further, the central oii'ce |0 comprises a plurality Aof groups of selectors, each serving a group of one hundred of the subscriber lines; the rst group of selectors, including the selector SIUG, serves the first group of one hundred subscriber lines, including the subscriber lines I3, I5 and |1 respectively extending to the subscriber substations TIO, TII and TI2, and is accordingly accessible, by way of a trunk extending thereto, to the respectively associated line switches I4, I6 and |8. Also, the central oflice I0 comprises a plurality of groups of connectors accessible to the selectors in the groups and having access to the corresponding groups of one hundred subscriber lines; the first group of connectors, including the connector |90, serves the rst group of one hundred subscriber lines, including the subscriber lines I3, I and I1, previously mentioned.

Also, the central cnice I0 comprises a group of trunk circuits terminating the trunk lines in the group extending to the distant exchange 20, the trunk circuit 300 terminating the trunk line 395; and another group of trunk circuits terminating the trunk lines in the group extending to the remote exchange 30, the trunk circuit 281 terminating the trunk line 286; and an operator switchboard 280. The operator switchboard 280 terminates a group of nine trunks, including the trunk 28|, terminated by a further group of trunk circuits, including the trunk circuit 282; the trunk 28| being terminated by the trunk circuit 282. Also, the central oilce I0 comprisesA a group of secondary trunks, including the secondary trunk 200. Each of the trunk circuits in the group, including the trunk circuit 300, isf provided with two incoming trunks or channels accessible to the selectors in the different groups; the trunk circuit 300 being provided with the incoming trunks 3|0 and 3|5 accessible to the se' lector S|00 in the rst group. Each of the secondary trunks in the group, including the secondary trunk 200, is provided with an incoming trunk accessible to the selectors in the differentl groups; the secondary trunk 200 being provided with the incoming trunk 2|0 accessible to the selector S|00 in the iirst group. Each of the trunk circuits in the group, including the trunk circuit 281, is accessible to the hunt switches incorporated in the secondary trunks 200, etc.; and each of the trunk circuits in the group, including the trunk circuit 282, is accessible to the hunt switches incorporated in the secondary trunks 200, etc.

The distant exchange 20 is of the automatic type comprising automatic switching apparatus 393 and serving a plurality of subscriber substations, including the subscriber substation TZI having the subscriber line 351 extending thereto. Similarly, the remote exchange 30 is of the automatic type comprising automatic switching apparatus 235 and serving a plurality of subscriber substations, including the subscriber substation T3| having the subscriber line 288 extending thereto.

Preferably, in the central oifice I0 each of the selectors is identical to the selector S|00 that comprises, as shown in Fig. 1, a Strowger mech--4 anism |80 including a wiper carriage supporting three sets of wipers and provided with three individually associated contact bank sections. The iii-st wiper set comprises the three wipers |8|a, {SIZ} and I8|c; the second wiper set comprises the four wipers |82a, |821), I82c and |82m; and the third wiper set comprises the four wipers 583e, |83b, |830 and |83m. Also, the Strowger mechanism |80 comprises a vertical magnet MIS I, a rotary magnet M|92 and a release magnet MI 94. Associated with the wiper carriage of the Strowger mechanism |80 are three sets of switch springs SH3, SIM and S||5 which are actuated when the wiper carriage is driven in the vertical direction away from its home position; as well as two sets of switch springs SIIG and S||1 which are actuated when the wiper carriage of the Strowger mechanism |80 is driven eleven steps in the rotary direction away from its home position. Also, theV selector SI00 comprises a relay group including a line relay RI I0 a hold relay RIZD, two transfer relays RI30 and RMU, a test relay RI45, a switch relay RI50 and two select relays R|60 and RI10. Further, the selector S|00 also comprises a discriminator switch |05 of the rotary type, including a double-ended wiper |96 provided with an associated contact bank and a magnet M|91 for driving the wiper |96 step by step in the clockwise direction. Associated with the wiper |96 is a set of switch springs S|99 which is actuated when the wiper noted is driven away from its home position.

Preferably, each of the secondary trunks is identical to the secondary trunk 200 which com prises, as shown in Fig. 2, a relay group including a line relay R220, a hold relay R230, a transfer relay R240, a test relay R250 and a lockout relay R260; as well as a hunt switch 210. The hunt switch 210 is of the rotary type including five wipers 21| to 215, inclusive, provided with individually associated contact banks, and a.; magnet M216 for driving the wipers noted step by step in the clockwise direction away from their home positions,

Preferably, each of the trunk circuits terminating the trunk lines extending between the central office I0 and the distant exchange 20 is identical to the trunk circuit 300 which comprises, as shown in Fig. 3, a repeater 335 and aI relay group including a reverse battery relay R320, an answer relay R330, a line relay R340-,-

a hold relay R345, a synchronizingrelay R350, a discriminating relay R363, a time release relay R365, Yand two timer relays R310 and R315. Also, the trunk circuit 33|) comprises a start pulse switch 393 of the rotary type, including two wipers 33 and 392 and a magnet M393 for driving the wipers noted step by step from their last` operated position.

Further, the central cii'ce I0 comprises an offlce timer 380. of the rotary type, including a wiper 38| provided with a magnet M382 for driving vthe wiper noted step by step from its last operated position; `as well as a timer mechanism 379. YThe timer mechanism 379 is connected to the oiice timer 3,83 and provides ground pulses thereto continuously at the expiration of each predetermined unit .time interval; while the cnice timer 3801 is commonly connected to the start pulse switches 393, etc., in .the various trunkcircuits 300, etc.

In the central omce Iii thev connectors in the various groups, such, for example, as the connector |90 in the rst one hundred line group, are of conventional Strowger construction, while the line switches I4, I6, I8, etc. are oi standardconstruction. Also, the trunk circuits 28?., etc. and 282, etc. in the respective groups may be of any suitable type. Finally, the operator switchboard 283 may be of any suitable type.

Furthermore, in the distant exchange 23 the switching apparatus 396 may be of any Well known type, such, for example, as Strowger apparatus; and in the remote exchange 3l] the switching apparatus 285 may be of any well known type, such, for example, as Strowger apparatus.

Local calls in the central ofce 10 Now assume that a call has been initiated at any subscriber substation in the central oilice I3, such, for exampleVas the subscriber substation TIO; when the call is initiated at the calling subscriber substation TIG the individually associated line switch I4 is controlled over the associated subscriber line I3 and operates to nd a trunk extending to an idle selector, such, for example, as the trunk |03 extending to the lselector Sicil. The selector SIl is marked as idle to the line switch I4 bythe application of battery potential by way of the lower winding of the transfer relay R|3Il and the set of switch springs SI I3 to the control conductor CIM of the trunk |33. Also, the line switch I4 operates to mark the subscriber line I 3 extending to the calling subscriber substation TIiI as busy to the connectors in the group, including the connector |90, having access thereto. When the trunk |33 is thus selected by the line switch I4, a loop circuit is completed from the calling subscriber substation TI by way of the associated subscriber line I3, the line switch I4 and the line conductors CIQI and CI62 of the trunk |33 to the line relay RI IQ in the selector SIM. More particularly, ground potential is applied by way of the contacts |32, the lower winding of the line relay RII and the contacts I 53 to the line conductor C|02 of the trunk and battery potential is applied by way of the upper winding of the line relay RI I0 and the contacts |5| to the line conductor CIBI of the trunk Ii). When this loop circuit is thus completed the line relay RI II) operates to complete, at the contacts II2, a circuit including the contacts |58 for operating the hold relay RIZEI. Upon operating, the hold relay RIZ completes, at the contacts |22, an yobvious .path .for applying ground .potential to thecontrol conductor CIM-,of the trunk |00, thereby to complete a circuit including the set of `switch springs'SI I3jfor energizing the lower winding of the transfer relay R|3Il in order toV cause the latter relay to operate. Also, the application of ground potential to the control conductor CI 04 retains the line switch. I4 in its operated position and marks the trunk I as busy tothe other line switches I6, I8, etc. Up.- on operating, the transfer relay RI33 completes, at the contacts |36, an obvious circuit for operating the transfer .relay RI4II. Also, the transfer relay RI3 completes, at the contacts I3I, an alternative path,including the contacts .IIof the set of switch springs SI I'I and the winding of the vdial tone transformer ||3, for applying ground potential by Way of the lower winding of the line relayRI IB to the line .conductorCIII2 of the trunk IBI); and interrupts, at the contacts |32, the previously traced original path for applying direct ground lpotential by way of the lower winding of the line relay RI II) to the line conductor-CI2 of the trunk |33. Accordingly, at this time the loop circuit extending between the calling subscriber substation TID and the line relay RI II) in the selector SIGO includes the winding of the dial tone transformer I I3, whereby dial tone current is returned thereover, indicating to the subscriber at the calling subscriber substation T I0 that hemaybegin the dialing of the nrst digit of the directory number of the called subscriber substation in the central oiiice I0.

Now assuming that the call is to Vbe extended tothe subscribed substation TII in the central cnice I3, the subscriber at the calling subscriber substation TIB dials the first digit 0 of the directory number of thexcalled subscriber substation Ti I, whereby the line relay RI I inthe selector SIGs follows the impulses of the rst digit mentioned. Each time the line relay RI III restores and then reoperates it interrupts and then re.- completes, at the contacts II2, the previously traced circuit for maintaining operated the hold relay RIZO, thereby to maintain the latter relay in its operated position during dialing since it is of the slow-to-release type. Also, each time the line relay RI I0 restores and then reoperates it completes and then interrupts, at the contacts II I, a circuit, including the contacts |58, |25 and |34, for energizing in multiple the upper winding of the transfer relay RI33 and the vertical magnet M|-9I of the Strowger mechanism |80, thereby to maintain operated the transfer relay RI3 subsequent to the interruption of the previously traced circuit for energizing the lower winding thereof, since the transfer relay R|30 is of the slow-to-release type. Accordingly, the vertical magnet MII operates and restores ten times, driving the wiper carriage of the Strowger mechanism ten steps in the vertical direction away from its home position. When the wiper carriage of the Strowger mechanism |80 is driven one step in the vertical direction away from its home position, the sets of switch springs SH3, SI I4 and SI I5 are actuated. More particularly, the set of switch springs SI I3 is actuated into disengagement, thereby to interrupt the previously traced circuit for energizing the lower winding of the transfer relay R|30, whereby the latter relay is rmaintained in its operated position only during dialing of the rst digit. The sets oi switch springs SII 4 and S||5 are actuated into engagement respectively to prepare circuits, traced hereinafter, for operating the rotary magnet MI92 and the release magnet MI'S of the Strowger mechanism |80. Finally, each time the line relay RI I restores and then reoperates it completes and then interrupts, at the contacts I amultiple circuit, including the contacts |58, |25 and |33, for operating the magnet M|91 of the discriminator switch |95, whereby the wiper |96 thereof is stepped ten steps in the clockwise direction away from its home position. When the wiper |96 of the discriminator switch |05 is driven one step in the clockwise direction away from its home position, the set of switch springs S|99 is actuated into engagement, for a purpose more fully explained hereinafter.

At the conclusion of the first digit the line relay Rl |0 is maintained in its operated position, thereby to retain operated the hold relay RI20 and to retain interrupted, at the contacts III, the multiple circuits for energizing the upper winding of the transfer relay R|30 and for energizing the vertical magnet MI9| of the Strowger mechanism |80, and for energizing the magnet M|91 of the discriminator switch |95. Also at this time the wiper carriage of the Strowger mechanism |80 occupies its tenth stepped position in the vertical direction. whereby the three wiper sets are disposed in vertical alignment with respect to the three associated sections of the contact bank but in rotary offset position with respect thereto. Moreover, at this time the wiper |96 of the discriminator switch |95 occupies its tenth rotary stepped position engaging the tenth contact in the associated contact bank; which contact is not wired to any controlled circuit, as explained more fully hereinafter. Shortly following the conclusion of the rst digit, the transfer relay RI30 restores to interrupt, at the contacts |3I, the previously traced path for connecting dial tone current into the loop circuit extending between the selector S|00 and the calling subscribed substation TIO, and to recomplete, at the contacts |32, the previously traced original loop circuit extending between the selector S|00 and the calling subscriber substation TIO. Also, upon restoring, the transfer relay RI30 interrupts, at the contacts |36, the previously mentioned circuit for maintaining operated the transfer' relay R|40, thereby to cause the latter relay to restore shortly thereafter since it is of the slow-to-release type.

Upon restoring, the transfer relay RI40 completes, at the contact |4I, a circuit, including the contacts |23, |41, |51 and |93 and the set of switch springs SII4, for operating the rotary magnet M|92 of the Strowger mechanism |80. Upon operating, the rotary magnet M|92 interrupts, at the contacts |93, the operating circuit therefor, whereby the rotary magnet MI92 restores to recoinplete, at the contacts |93, the operating circuit therefor. Accordingly, the rotary magnet MI92 operates buzzer fashion in order to drive the wiper carriage of the Strowger mechanism |80 step by step in the rotary direction until a. trunk extending to an idle connector in the previously selected group is selected by the first Wiper set supported by the wiper carriage thereof. Assuming that the trunk |05 extending to the connector |90 is the iirst idle trunk in the previously selected group, the rotary magnet MI92 operates and restores intermittently in order to drive the wiper carriage in the rotary direction until the first wiper set, including the wipers IBIa, |8|b and |8|c engage the contacts in the first section of the associated contact bank terminating the conductors C|06, C|01 and C|08 of the trunk |05; the .trunk |05 being marked as idle to the selector S|00 by the application of battery potential to the control conductor C| 08 thereof. When the selector SI00 operates in the above described manner to select the trunk |05 extending to the connector |90, a circuit, including the contacts I2|, |61 and |11, the control wiper |8Ic of the rst wiper set, and the control conductor CI08 of the trunk |05, is completed for operating the test relay RI45. Upon operating, the test relay R|45 interrupts, at the contacts |41, the previously traced circuit for operating intermittently the rotary magnet MI92 of the Strowger mechanism and completes, at the contacts |46, a circuit including the contacts |23 for operating the switch relay RISO. Upon operating, the switch relay R|50 completes, at the contacts |56, a holding circuit, including the contacts |22, for maintaining itself operated; and completes, at the contacts |55, a path, including the contacts |22, |61 and |11, for applying ground potential to the control 'wiper I8|c of the rst wiper set in order to cause ground potential to be applied to the control conductor C|08 of the trunk |05, thereby to effect seizure of the connector |90. Also, the switch relay RI 50 interrupts, at the contacts I5| and |53, the previously traced loop circuit extending between the calling subscriber substation TI 0 and the line relay PI I0 in the selector SI00; and completes, at the contacts |52 and |54, an alternative loop circuit extending between the calling subscriber substation TIO and the connector |90. The alternative loop circuit mentioned extends from the line conductors C|0I and C|02 of the trunk |00 by way of the contacts |52, |54, I6|, |63 and I1|, |13, the line wipers |8|a and I8Ib of the first wiper set and the line conductor C 06 and C 01 of the trunk |05. When the above-traced original loop circuit extending between tlie calling subscriber substation T|0 and the line relay RIID in the selector S|00 is thus interrupted, the line relay RIID restores; and finally, upon operating, the switch relay R|50 interrupts, at the contacts |58, the previously traced circuit for maintaining operated the hold relay RIEU, whereby the latter relay restores shortly thereafter it being of the slow-to-release type. Also, upon operating, the switch relay R|50 completes, at the contacts |55, a path, including the contacts I2| and |22, for short-circuiting the winding of the test relay R|45 in order to cause the latter relay to restore. At this time the selector S|00 has operated to select the trunk |05 extending to the connector |90, and the switch relay R|50 in the selector SIDO is retained in its operated position by virtue of a completed holding circuit therefor, including the grounded control conductor CI08 of the trunk |05; ground potential in the connector being applied to the control conductor CI08 of the trunk |05 subsequent to the seizure of the connector |99. The path mentioned extends from the grounded control conductor C 08 of the trunk |05 by way of the control wiper I8|C of the first wiper set, the contacts |11, |61, |55 and |56, and the winding of the switch relay R|50 to battery.

At this time the connector |90 is rendered responsive to the second and third digits of the directory number of the called subscriber substation T| I; which digits are dialed at the calling subscriber substation T 0 in order to cause operation of the connector |90 to select the subscriber line I5 extending to the called subscriber substation T||. The subsequent operation of the connector |90 depends upon the idle or busy condition of the called subscriber substation vTII and takes place in a conventional manner. Assuming that the called subscriber substation Tll is v.idle at this time the connector |98 operates when the call is answered at the called subscriber substation Till `to complete a ytelephone connection thereto from the calling subscriber substation Tlil. Also the connector |99 operates to mark the subscriber line l extending to the called subscriber substation T| i as busy to the other connectors in the same gro-up having access thereto.

Subsequently, at the conclusion of the connection, when the subscriber at the calling subscriber substation T le replaces the receiver of the telephone instrument thereat upon its associated switchhook, the loop circuit extending therefrom by way of the line switch l5 and the selector SIB!) to the connector ISU is interrupted, thereby.

to bring about the release of the connector |99; whereby-the subscriber line l5 extending to the called subscriber substation T| is marked as idle to the connectors in the same group having access thereto, assuming that the subscriber at the called subscriber substation Tl has replaced the receiver of the telephone instrument thereat upon its associated switchhook at this time'. When the connector |99 is thus released ground potential is removed from the control conductor CIGS of the trunk |05, thereby to interrupt the previously traced circuit for maintaining operated the switch relay R|59 in the selector Sls. Upon restoring, the switch relayRI completes, at the contacts 158, a circuit, including the contacts Hi, |24 and |42, and the set of switch springs SM5, for operating the release magnet M|94, whereby the wiper carriage of the Strowger mechanism |89 'is released and returned to its home position. When the Strowger mechanism 13|) is thus released, the sets of switch springs SI I3, Si I4 and SI l5 are actuated. More particularly, the sets oi switch springs SI i3 is actuated into engagement, thereby to complete the previously traced path for applying battery potentiall by way of the lower winding of the transfer relay Rlil to the control conductor Clli Vof the trunk Hill; and the set of switch springs SI l5 is actuated into disengagement, thereby to interrupt the above-traced circuit for operating the release magnet M! 94 of the Strowger mechanism |83. Also, upon restoring, the switch relay Rl completes, at the contacts |58, a multiple circuit, including the contacts |24 and M2, the set of switch springs SL99, and the contacts -|98, for operating the magnet M|91 of the discriminator switch 95. Upon operating, the magnet M191 interrupts, at the contacts |98,'the operating circ-uit therefor, whereby the magnet M |9'l restores in order to recomplete, at the contacts |98, the operating circuit therefor. Accordingly. the magnet M191 operates buzzer fashion, thereby to drive the wiper |96 of the discriminator switch |95 step by step in the clockwise direction back into its home position. When the wiper |96 of the discriminator switch |95 is driven back into its home position, the set of switch springs S|99 is actuated into disengagement, thereby to interrupt the above-traced circuit for operating the magnet MIS'L At this time the selector Sltii is completely released and marked as idle, by the application of battery potential to the control conductor Clfi of the trunk |99, to the line switches le, l5, i8, etc. When ground potential is removed from and battery potential is reapplied to the control conductor CHM of the trunk lill), the line switch I4 is restored in order l0 to mark. the subscriber line I3 extending lto the subscriber substation Tl!) as idle to the connectors in the group, including the connector |90, having access thereto.

Trunk calls from the central o'lce 10 to the distant exchange 20 At the outset it is noted that the subscriber substations rendered restricted service, such, for example, as the subscriber substation Tl'in the central cnice l0, are not permitted to extend connections to the distant exchange 213 `and specifically that such stations do not have facility for controlling operation oi the selectors Smil, etc. in order to bring about this result, as explained more fully hereinafter in conjunction with the extension of connections from subscriber substations rendered non-restricted service and subscriber substations rendered limited service in the central oilce Ii). Specifically, a subscriber substation rendered restricted service, such for example, as the subscriber substation T10 in the central ofce iii, must iirst extend a connection to the operator switchboard 280 in the central office I0, in a manner more fully explained hereinafter, and permit the operator at the switchboard 2% to complete the connection to a called subscriber substation in the distant exchange 29.

Considering nowthe extension of a call from a subscriber substation vrendered non-,restricted service, such, for example, as the subscriber substation T|2 in the central oiice lil, to a'called subscribei'substation, such, for example, as the subscriber substation T2| in the distant exchange 28, the subscriber at the calling subscriber substation T2 rst initiates the call in order to control the line switch. ri8 over the associated subscriber line il, whereby the line switch I8 selects a trunk extending to an idle selectonsuch, for example, as the trunk |09 extending to the selector SIM. The subscriber at the ycalling subscriber substation T|2 then dials the rst digit Y of the directory number of the called subscriber substation T2| in the distant exchange 2?.v It will, of course, be understood that the subscriber at the calling subscriber substation T|2 merely operates the dial thereat utilizing k,the eleventh digit nger hole therein, whereby the dial mentioned causes twelve impulses in `a group to be transmitted therefrom over the subscriber line il, the line switch i8 and the trunk |99 to the selector Slim. The selector Smil responds to the digit Y in a manner substantially identical l' to that previously explained. However, since the Strowger mechanism |89 is capable of only ten steps in the vertical direction, the eleventh and twelfth impulses transmitted to the vertical magnet MISI thereof are without effect and, in fact, the wiper carriage of the Strowger mechanism .is driven `ten steps in the vvertical direction away 'from its home position. However, the magnet IST of the discriminator switch is capable of responding to the eleventh and twelfth impulses of the digit Y, in order to cause the wiper L95 thereof to engage the twelfth contact in the associated contact bank terminating the conductor 'extending to the lower winding of the selector relay RUG. Accordingly, in the present example, at the conclusion of the lrst digitf, when the transfer relay RASS restores, it completes, at the contacts |35, a circuit in multiple to the winding of the hold relay RIZ!! and including the contacts |58 and ||2 for applying ground potential to the wiper .|96 of the dis- 1l criminator switch |95. This application of ground potential to the wiper |90 of the discriminator switch |95 completes an obvious circuit for energizing the lower winding of the select relay R|10, thereby to cause the latter relay to operate and complete, at the contacts |13, a holding circuit, including the contacts |22, for energizing the upper winding thereof. Also, the switch relay R| interrupts, at the contacts I1 I, |13 and |11, the previously traced connections between the selector SISO and the wipers I8Ia, |8| b and I 8| c of the rst wiper set of the Strowger mechanism |80; and completes, at the contacts |12, |14, |16 and |18, connections between the selector S|00 and the wipers |82a, |82b, |821n and |B2c of the second wiper set of the Strowger mechanism |80. Shortly following the restoration of the transfer relay RI30, the transfer relay R|40 restores in order to initiate operation of the rotary magnet |92 of the Strowger mechanism |80, in the manner previously explained,

whereby the selector S|00 operates to select an 4 idle trunk in the previously selected group, including the incoming trunk 3|0; which trunks extend to the group of trunk circuits, including the trunk circuit 300.

Assuming that the trunk 3|0 is the rst idle trunk in the group previously selected by the selector SIOO, operation of the rotary magnet MI92 is arrested incident to operation of the test relay R|45 when the second Wiper set of the Strowger mechanism |90 engages the contacts in the second section of the contact bank terminating the conductors of the trunk 3|0; the trunk 3| 0 being marked as idle to the selector S|00 by the application of battery potential upon the control conductor C3|4 thereof. More particularly, battery potential is connected by way of the lower winding of the answer relay R330 directly to the control conductor C3| 4 of the trunk 3|0. Upon operating, the test relay R|45 causes operation of the switch relay Rl50, as previously noted, thereby to interrupt, at the contacts |5I and |53, the original loop circuit extending between the calling subscriber substation TI2 and the line relay RI |0 in the selector SI00; and to complete, at the contacts |52 and |54, an alternative loop circuit extending between the calling subscriber substation T|2 and the line relay R340 in the trunk circuit 300. More specifically, ground potential is connected by way of the lower winding of the line relay R340, the contacts 324 and the winding 338 of the repeater 335 to the line conductor C3I2 of the trunk 3|0, and battery potential is connected by way of the upper winding of the line relay R340, the contacts 322 and the winding 335 of the repeater 335 to the line conductor C3| I of the trunk 3|0; the line conductors C3|| and C3|2 of the trunk 3| 0 are connected by way of the line wipers |82a, |8212 of the second wiper set of the Strowger mechanism |80, and the contacts |12, |14, ISI, |63 and |52, |54 to the line conductors C|0| and C|02 of the trunk |00; and thence to the calling subscriber substation TI2.

When this alternative loop circuit is thus completed the line relay R340 in the trunk circuit 300 operates to complete, at the contacts 34|, an obvious circuit for operating the hold relay R345. Also, the line relay R340 completes, at the contacts 342, a bridge including the windings 331 and 339 of therepeater 335, and the upper winding of the answer relay R330 across the line conductors of the trunk line 385 eX- tending to the switching apparatus 395 in the distant exchange 20, whereby the switching apparatus 336 is seized and conditioned to be responsive to digits transmitted thereto over the trunk line 395. Upon operating, the hold relay R345 completes, at the contacts 34B, an obvious path for energizing the lower winding of the answer relay R330. However, the latter relay does not operate at this time as it is of the polarized type, and the upper winding thereof must be energized in the reverse direction over the trunk line 395 in order to effect operation thereof. Further, the hold relay R345 completes, at the contacts 346, an obvious path for applying ground potential to the control conductor C3|4 of the trunk 3|0, thereby to complete a holding circuit, including the control wiper |82c of the second wiper set of the Strowger mechanism |80, the contacts |18, |61 and |55, the conductor C|04 and the contacts |56, for maintaining operated the switch relay R| in the selector S|00. The application of ground potential to the control conductor C3|4 of the trunk 3|0 completes a path, including the contacts 356 and the winding of the discriminating relay R360, for applying ground potential to the control conductor C3I9 of the trunk 3|5. The application of ground potential to the control conductor C3|4 of the trunk 3|0 and to the control conductor C3|9 of the trunk 3|5 marks the trunks 3| 0 and 3I5 as busy to the selectors S|00, etc. having access thereto. Also, this application of ground potential upon the control conductor CI04 of the trunk |00 maintains the line switch |8 individual to the calling subscriber substation T|2 in its operated position, and also completes an obvious multiple circuit, including the contacts |19, for maintaining operated the select relay R|10 in the selector S|00.

At this time the proviously traced loop circuit is completed between the calling subscriber substation T|2 and the line relay R340 in the trunk circuit 300, and the previously traced loop circuit is completed between the upper winding of the answer relay R330 in the trunk circuit 300 and the switching apparatus 396 in the distant exchange 20. The subscriber at the calling subscriber substation TI2 then proceeds to dial the second digit of the directory number of the called subscriber substation TZI in the distant Yexchange 20, whereby the line relay R340 in the trunk circuit 300 follows, repeating at the contacts 342, the impulses of the second digit over the trunk line 395 to the switching apparatus 355 in the distant exchange 20. The hold relay R345 being of the slow-to-release type remains operated during impulsing by the line relay R340. The subscriber at the calling subscriber substation TIZ in the central oice I0 then dials the remainder of the digits of the directory number of the called subscriber substation T2| in the distant exchange 20, in order to bring about operation of the switching apparatus 390 to select the subscriber line 391 extending thereto, all in a conventional manner. The subsequent operation of the switching apparatus 395 depends upon the idle or busy condition of the called subscriber substation T2| at this time; and assuming that the called subscriber substation T2| is idle when the call is answered thereat, the switching apparatus 390 operates in order to complete a connection thereto and to effect the reversal of polarity over the trunk line 395. When the polarity of the trunk line 355 is thus reversed the upper winding of arianna 13 the answer relay R33!) in the trunk circuit .300 tis poled to operate; .and upon operating, "com- .for operating .the reverse battery relay R329. Upon operating, the vreverse battery relay R32-0 reverses, at the contacts 32|, .322, i323 and 324, the vpolarity of the vloop circuit Yextending lbetween the calling subscriber. .substation \T-|2 in the central cnice .man-d the iine relay R34'0`in 'the trunk circuit 399,' which reversal lof polarity over the loop circuit 'mentioned conditions the `.meter MIZ 'connected to :theline switch I8 to be operated, in a manner more .fully explained hereinafter.

At this point itis noted that the timermechanism 319 operates continuously'to transmit iintermittently on a timed basis groundimpulse's to the magnet M382 of 'the Yoiiice timer 39.9, wherebythe magnet M382 operates and restores lintermittentlyn Each time the magnet y'M382 operates and 'restores it interrupts and-then recompletes, vat the contacts 33|, an .obvious circuit pletes, at the contacts 383, an Aobvious path for .applying .ground potential to the wiper v33| of the ofiice .timer .389; .and also drives the 'wiper 38| of the .cnice timer 1390 an additional lstep 'in- 'the rotary direction. Accordingly, .at an-y given time the wiper 385| vof the office timer "389 may engage any contact in 'the associated Vcontact bank, and it is .thus necessary to synchronize the associated ystart pulse switch 399 iin the trunk circuit 309 'with the Aoffice timer SSB-at this time.

Continuing now with Ithe operation 'of the trunk circuit 390, also uponoperating, the reverse-bat- "tery relay R329 completes, at the contacts 325, :a circuit including .the cor-itacts 353 and 394 `for I operating the magnet M393 of the "start pulse switch 399, thereby to cause the 'magnet M393 to operate vand interrupt, ,at the contacts 394,`the .operating circuit therefor. The magnet .M393

then restores to recomplete, 'at the `.contacts 394, ,v

the operating circuit therefor, whereby the magnet M393 'operates buzzer fashion in order to drive the wipers 39'! and 392 'of the start "pulse switch '39.9 step by step in the rotary direction until the wiper 39| of the start pulse .switch 399 engages the contact in the associated contact bank terminating the conductor strapping .the contact mentioned to the contact engaged by the wiper 38| of the voiiice timer 389 iat this time; lwhereupon there is completed .a circuit .for

position. However, the magnet M393 l.of the start"y f pulse switch 399 is not .operated .due Vto the high series resistance of the upper winding ofthe synchronizing relay R350. The previously mentioned circuit for energizing the lower winding of the synchronizing relay R350 extends, when completed, from ground by way of the contacts 383, the wiper 38| and the engaged contact in 5 the associated contact bank, .the wiper 39| ands:

"the engaged contact in the associated contact?? bank. the `contacts 32e` and 356, and .the 'lower rwinding of R359 to battery. At the conclusion of the predetermined unit time interval mentioned the magnet .M382 of the oi'ce timer 13.89 again :operates .and restores, in -orderto ici-rive the wiper 38| thereofl ian additional fstep'i-n'the rotary di- :rection and into :engagement with the contact in the associated .contact bank that is strapped to the .contact in `the contactb'an'k engaged by the Wiper 392 of the .start pulse switch- 399, .whereby ground A.potential is applied by way of 'the contact 383, the wiper 4S8|and the engaged contact inthe :associated contact'banle'the strap z-mentioned, and the wiper 392 and the eng-aged contact in the :associated `contact bank,. a-nd the contacts .s352- 'to fthe meter conductor' C313 of the trunk 311i. 'This application of ground potential to the meter conductor `C313 ofthe trunk 3| completes a circuit, including the contacts '35 for energizingthe-upper winding of the timer relay-R310, thereby to cause the latter relay 'to operate and complete, at the contacts 3l a hold'- ing circuit, including `-the contacts 343, for Aenergizing the lower winding thereof. Also, this ap- `-pl-ication of lground lpotential -to the meter *conductor C313 of vthe trunk 3H] completes a path, including the meter wiper 192m -of the second Wiper set-of the Strowger mechanism |89 and the 'contacts H6 =and |65, for applying Y'ground potential to the vmeter conductor C|93- of the Vtrunk |39; which application Aof ground vpotential to .the meter conductor C|93 -of the 'trunk |99 effects operation of lthe :meter M12 connected vto the `line switch i8 'associated with the calling subscriber substation T-I-Zlin'the central oice I9.

A-t theconclusion of nineadditional vunit time intervals the magnet M382 lhas driven "the :Wiper 38| of the oiic'e timer 323|) vagainto' engage the f'contafct in the associated contact "bank that vis strapped to fthecontact inthe contact bankengaged 'by the wiper 39| of the start pulseswitch 399; which operationy is without effect in vthe present vexample since vthe discriminating relay R390 in the trunk circuit 390 occupies yits restored position. Subsequently, at the conclusion of an additional unit time interval, lthe magnet M382 ldrives the wiper 38| of the oiice 'timer 389 again to engage the Contactin the 'associated contact bank that is strapped to the contact in the contact bank `engaged by the Vwiper 392 of thestart 'Lpulse switch 399, thereby again to apply ground potential to 'the meter 'conductor C313 in the trunk 3N] and, consequently., to the meter 'conductor C'l3 inthe trunk |99; whereby the meter M|2 connected Ato theline switch |8 individually I.associated With the callin-g subscriber substation T12 is again operated. :'l'his sequence of operation continues, whereby `at the V'conclusion of each `ten Aunit time intervals the meter MIZ connected to the line switch' i3 individually associatedwith the calling subscriber substation T|2 is 'reoperated in view .of 'the foregoing it will be appreciated that the calling 'subscriber Vsubstation TIZr rendered non-restricted service in the central ofce 'I9 mayextend a connection toa called subscriber substasubscriber at the calling Ysubscriber 'substation T12 in the central cnice 4|11 'replaces the receiver 'of the vtelephone'instrument thereat upon its associated switchhook, the previously traced yloop circuit 'extending 4therefrom by way ofthe selector .SIUIJ to the line relay H3819' in .the .trunk ciricuit 300 is interrupted in order to cause the latter relay to restore. Upon restoring, the line relay R340 interrupts, at the contacts 342, the previously traced loop circuit, including the trunk line 335 extending to the switching apparatus 386 in the distant exchange 20, thereby to cause the switching apparatus 396 to release, marking the subscriber line 391 extending to the called subscriber substation T2| in the distant exchange as idle, assuming that the subscriber at the called subscriber substation T2| has replaced the receiver of the telephone instrument thereat upon its associated switchhook at this time. Also, when the line relay R340 interrupts, at the contacts 342, the loop circuit mentioned, the upper Winding of the answer relay R330 is deenergized, causing the latter relay to restore. Further, the line relay R340 interrupts, at the contacts 34|, the previously mentioned curcuit for maintaining operated the hold relay R345 in order to cause the latter relay to restore shortly thereafter, it being of the slow-to-release type. Upon restoring, the answer relay R330 interrupts, at the contacts 33|, the previously mentioned circuit for maintaining operated the reverse battery relay R320. Upon restoring, the hold relay R345 interrupts, at the contacts 346, the previously mentioned path for applying ground potential to the control conductor C3|4 of the trunk 3|0, thereby to interrupt the previously traced holding circuit for energizing the lower winding of the timer relay R310 and the previously traced multiple holding circuit for energizing the upper winding of the synchronizing relay R350 in series with the magnet M393 of the start pulse switch 390, whereby the timer relay R310 and the synchronizing relay R350 restore. Upon restoring, the reverse battery relay R320 restores, at the contacts 32|, 322, 323 and 324, the polarity of the line conductors C3|I and C3I2 of the trunk 3I0 with respect to the line relay R340. At this time the trunk circuit 300 is completely released. Also, when ground potential is removed from the control conductor C3|4 of the trunk 3|0, the previously traced holding circuit for maintaining operated the switch relay R| in the selector S|00 is interrupted, whereby the latter relay restores in order to bring about the release of the selector S|00, in the manner previously ex'- plained. In this connection it is noted that the previously traced holding circuit for energizing the upper winding of the select relay RI'I0 is arranged in multiple with the holding circuit for energizing the winding of the switch relay RI50, whereby the select relay RII0 restores incident to the restoration of the switch relay R|50. At this time the selector S|00 is completely released and available for further use. When the selector SI 00 is thus released the line switch I8 is restored, marking the subscriber line II extending to the subscriber substation T|2 in the centrall omce I0 as idle to the connectors in the group, including the connector |90, having access thereto.

Considering now the extension of a call from a subscriber substation rendered limited service, such, for example, as the subscriber substation TII in the central oiiice I0, to a called subscriber substation, such, for example, as the subscriber substation T2| in the distant exchange 20, the subscriber at the calling subscriber substation TI I first initiates the call in order to control the line switch I6 over the associated subscriber line I5, whereby the line switch I6 selects a trunk extending ,to an idle selector, such, for example, as the trunk |00 extending to the selector S|00.

16 The subscriber at the calling subscriber substation TII then dials the first digit X of the directory number of the called subscriber substation T2| in the distant exchange 20. It will. of course, be understood thatv the subscriber at the calling subscriber substation TI I merely operates the dial thereat utilizing the eleventh digit'nger hole therein, whereby the dial mentioned causes eleven impulses in a group to be transmitted therefrom over the subscriber line I5, the line switch I6 and the trunk |00 to the selector SI00. The selector S|00 responds to the digit X in a manner substantially identical to that previously explained. However, since the Strowger mechanism is capable of only'ten steps in the vertical direction, the eleventh impulse transmitted to the vertical magnet M|9| thereof is without effect and, in fact, the wiper carriage of the Strowger mechanism |80 is driven ten steps in the vertical direction away from its home position. However, the magnet MIS'I of the discriminator switch is capable of responding to the eleventh impulse of the digit X, in order to cause the wiper |96 thereof Vto engage the eleventh contact in the associated contact bank terminating the conductor extending to the lower winding of the select/or relay R|60. Accordingly, in the present example, at the conclusion of the rst digit X, when the transfer relay RI30 restores, it completes, at the contacts |35, a circuit in multiple to the winding of the hold relay R|20 and including the contacts |58 and II2 for applying ground potential to the wiper |95 of the discrirninator switch |95. This application of ground potential to the wiper |96 of the discriminator switch |95 completes an obvious circuit for energizing the lower winding of the select relay R|60, thereby to cause the latter relay to operate and complete, at the contacts |59, a holding circuit, including the contacts |22, for energizing the upper winding thereof. Also, the switch relay R|60 interrupts, at the contacts |6I, |63 and |61, the previously traced connections between the selector S|00 and the wipers I8Ia, |8|b and |8|c of the iirst wiper set of the Strowger mechanism |80; and cornpletes, at the contacts |52, |64, |66 and |68, connections between the selector S I 00 and the wipers |83a, |8312, I83m and |830 of the third wiper set of the Strowger mechanism |60. Shortly following the restoration of the transfer relay RI30, the transfer' relay R|40 restores in order to initiate operation of the rotary magnet M|92 of the Strowger mechanism |80, in the manner previously explained, whereby the selector S|00 operates to select an idle trunk in the previously selected group, including the incoming trunk 3 I 5; which trunks extend to the group of trunk circuits, including the trunk circuit 300.

Assuming that the trunk 3|5 is the first idle trunk in the group previously selected by the selector SI00, operation of the rotary magnet M|92 is arrested incident to operation of the test relay RI45 when the third wiper set of the Strowger mechanism |80 'engages the contacts in the third section of the contact bank terminating the conductors of the trunk 3|5; the trunk 3|5 being marked as idle tb the selector SIDD by the application of battery potential upon the control conductor C3|9 thereof. More particularly, battery potential is connected by way of the lowerwinding of the answer relay R330, the contacts 365 and the winding of the discriminatingv relay R360 to the control conductor C3|9; whereby the discriminating relay 17 R360 in the trunk circuit 300 operates in series with the test relay R|45 in the selector Sl 00.

Upon operating, the test relay R|45 causes operation of the switch relay R|50, as previously noted, thereby to interrupt, at the contacts |5| and |53, the original loop circuit extending between the calling subscriber substation TII and the line relay R| I9 in the selector SIEJ; and to complete, at the contacts 52 and |54, an alternative loop circuit extending between the calling subscriber substation T and the line relay R340 in the trunk circuit 390. More specically, ground potential is connected by way of the lower winding of the line relay R340, the contacts 324 and the winding 339 of the repeater '335 to the line conductor 03|? of the trunk 3I5,

and battery potential is connected by way of the upper winding of the line relay R340, the contacts 322 and the winding 335 of the repeater 335 to the line conductor C3|5 of the trunk 3|5; the line conductors C3|6 and C3|'| of the trunk 3|5 are connected by way of the line wipers |0311, |83?) of the third wiper set of the Strowger mechanism |80, and the contacts |52, |34 and |52, |54 to the line conductors C|0| and C|92 of the trunk |99; and thence to the calling subscriber substation TI When this alternative loop circuit is thus completed the line relay R340 in the trunk circuit 300 operates to complete, at the contacts 34|, an obvious circuit for operating the hold relay R345. Also, the line relay R340 completes, at the contacts 342, a bridge including the windings 33'! and 339 of the repeater 335, and the upper winding of the answer relay R339 across the line conductors of the trunk line 395 extending to the switching apparatus 395 in the distant exchange 20, whereby the switching apparatus 395 is seized and conditioned to be responsive to rigits transmitted thereto over the trunk line 395. Upon operating, the hold relay R345 completes, at the contacts 345, an obvious path for energizing the lower winding of the answer relay R330. However, the latter relay does not operate at this time as it is of the polarized type, and the upper winding thereof must be energized in the reverse direction over the trunk line 395 in order to eiect operation thereof. Further, the hold relay R335 completes, at the contacts 346, an obvious path for applying ground potential to the control conductor C3|4 of the trunk 3| 0, thereby to complete a holding circuit, including the contacts 355, the winding ci the discriminating relay R360, the control conductor C3|9 of the trunk 3|5, the third control wiper |030 of the third wiper set of the Strowger mechanism |80, the contacts |63 and |55, the conductor CI 04, and the contacts |53, for maintaining operated the discriminating relay R350 in the trunk circuit 300 and the switch relay R|50 in the selector SIUE). The application of ground potential to the control conductor C3|5 of the trunk 3|0 and to the control conductor C3I9 of the trunk 3|5 mark the trunks 3I9 and 3|5 as busy to the selectors Sl, etc. having access thereto. Also, this application of ground potential upon the control conductor CIBLE of the trunk maintains the line switch I individual to the calling subscriber substation TI I in its operated position and completes an obvious multiple circuit, including the contacts |99, for maintaining operated the select relay R|B0 in the selector-SIM.

At this time the previously traced loop circuit is completed between the calling subscriber substation T| and the line relay R340 in the trunk circuit 300,and the previously traced loop circuit is completed between the upper winding of the answer relay R330 in the trunk circuit 300 and the switching apparatus 396 in the distant exchange 20. The subscriber at the calling subscriber substation TII then proceeds to dial the second digit of the directory number of the called subscriber substation T2| in the distant exchange 29, whereby the line relay R349 in the trunk circuit 300 follows, repeating at the contacts 342, the impulses of the second digit over the trunk line 395 to the switching apparatus 399 in the distant exchange 20. The hold relay R345 being of the slow-to-release type remains operated during impulsing by the line relay R340. The subscriber at the calling subscriber substation TII in the central oflice I0 then dials the remainder of the digits of the directory number of the called subscriber substation T2| in the distant exchange 20, in order to bring about operation of the switching apparatus 396 to select the subscriber line 391 extending thereto, all in a conventional manner. The subsequent operation of the switching apparatus 399 depends upon the idle or busy condition of the called subscriber substation T2I at this time; and assuming that the called subscriber substation T2| is idle when the call is answered thereat, the switching apparatus 396 operates in order to complete a connection thereto and to effect the reversal of polarity over the trunk line 395. When the polarity of the trunk line 395 is thus reversed the upper winding of the answer relay R330 in the trunk circuit 309 is poled to operate; and upon operating, completes, at the contact 33|, an obvious circuit for operating the reverse battery relay R320. Upon operating, the reverse battery relay R320 reverses, at the contacts 32|, 322, 323 and 324, the polarity of the loop circuit extending between the calling subscriber substation TII in the central office I0 and the line relay R349 in the trunk circuit 300; which reversal of polarity over the loop circuit mentioned conditions the meter MII connected to the line switch I6 to be operated, in a manner more fully explained hereinafter.

Also, upon operating, the reverse battery relay R329 completes, at the contacts 325, the previously traced circuit for operating the magnet M393 of the start pulse switch 390 in order to cause intermittent operation thereof, in the manner previously explained, whereby the wipers 39| and 392' of the start pulse switch 390 are driven step by stepA in the rotary direction until the wiper 39| thereof engages the contact in the associated contact bank terminating the conductor strapping the contact mentioned to the contact engaged by the wiper 38| of the ofce timer 380 at this time, thereby to bring about operation of the synchronizing relay R350 and the consequent arresting of further operation of the magnet M393 of the start pulse switch 390, all in the manner previously explained. At this time the synchronizing relay R350 is held in its operated position by way of the previously traced holding circuit for energizing the upper winding thereof; and at the conclusion of the predetermined unit time interval mentioned the magnet M382 of the oice timer 380 again operates and restores, in order to drive the wiper 33| thereof an additional step in the rotary direction and into engagement with the contact in the associated contact bank that is strapped to the contact in the contact bank -engaged by the wiper 392 of the start pulse switch 390, whereby ground potential is applied by way of the contact 383, the wiper 38| and the engaged operate and complete, at the contacts Y31 1, a holding circuit, including the contacts 346, for energizing the lower winding thereof. Also, this application of ground potential to the meter conductor C318 of the trunk 315 completes a path, including the meter wiper 183m of the third wiper set of the Strowger mechanism 186 and the contacts 166, for applying ground potential to the meter conductor C103 of the trunk 133; which application of ground vpotential to the meter conductor C103 of the trunk 100 effects operation of the meter M11 connected to the line switch 15 associated with the calling subscriber substation T11 in the central office 10.

At the conclusion of nine additional unit time intervals the magnet M382 has driven the wiper 381 of the office timer 380 again to engage the contact in the associated contact bank that is strapped to the contact in the contact bank engaged by the wiper 391 of the start pulse switch 393, thereby to complete a path, including the contacts 383, for applying ground potential to the wiper 391. This application of ground potential to the wiper 301 of the start pulse switch 390 completes a circuit, including the contacts 326, 355, 361, 312 and 318, for energizing the lower winding of the timer relay R315, whereby the latter relay operates through its first step to complete, at the contacts 316, a substantially identical path, including the contacts 346, for short-circuiting the upper winding thereof, the timer relay R315 being of the two-step type. Subsequently, at the conclusion of an additional unit time interval, the magnet M382 drives the wiper 331 of the oice timer 380 again to engage the contact in the associated Contact bank that l is strapped to the contact in the contact bank engaged `by the wiper 382 of the start pulse switch 390, thereby again to apply ground potential to the meter conductor C318 of the trunk 315 and, consequently, to the meter conductor C103 of the trunk 100, whereby the meter M11 connected to the line switch 16 individually associated with the calling subscriber substation T11 is again operated. Also, at this time, when the wiper 381 of the cnice timer 380 disengages the contact in the associated contact bank that is strapped to the contact in the contact bank engaged by the wiper 391 of the start pulse switch 390, the previously traced path for short-circuiting the upper winding of the timer relay R315 is interrupted, whereby the upper and lower windings of the timer relay R315 are energized in series over a circuit including the contacts 316 and 346. When the timer relay R315 is thus energized it operates through its second step.

At the conclusion of nine additional unit time intervals the magnet M382 has driven the wiper 381 of the oice timer 380 again to engage the contact in the associated contact bank that is strapped to the contact in the contact bank engaged by the wiper 391 of the start pulse switch 390, thereby to complete a circuit, including the contacts 383, the wipers 381 and 391 mentioned, the contacts 326, 355, 361, 312 and 311, for operating the time release relay R365. Upon operating, the time release relay R365 completes, at the contacts 361, a holding circuit for maintaining it operated, including the contacts 346; and interrupts, at the contacts 36E, the previously traced holding circuit for maintaining operated the discriminating relay R363 in the trunk circuit 330 and the switch relay R150 in the selector S100. The switch relay R150 in the selector S then restores in order to effect the release of the selector S100 and the trunk circuit 303, and the consequent release of the established connection between the calling subscriber substation T1 1 in the central office 10 and the called subscriber substation T21 in the distant exchange 20, all in the manner previously explained. In view of the foregoing it will be appreciated that the calling subscriber substation T1 1 rendered limited service in the central office 10 may extend a connection to a called subscriber substation in the distant exchange 20, and that the associated meter M1 1 is operated shortly following the answering of the call at the called subscriber substation in the distant exchange 20 and again at the expiration of ten unit time intervals. However, in the event that the established connection between the calling subscriber substation T11 in the central oflice 10 and the called subscriber substation in the distant exchange 20 persists for an additional nine unit time interval, the connection is automatically released by virtue of the operation of the time release relay R365 in the trunk circuit 300 as explained above.

Of course, it will be understood that the normal release of the established connection takes place when the subscriber at the calling subscriber substation T11 in the central ofce 10 replaces the receiver of the telephone instrument thereat upon its associated switchhook, interrupting the previously traced loop circuit extending therefrom by way of the selector S100 to the line relay R343 in the trunk circuit 300, whereby the latter relay restores. Upon restoring, the line relay R340 eiects the release of the switching apparatus 395 in the distant exchange 20, the trunk circuit 300 and the selector S100, all in the manner previously explained. In this connection it is noted that when the hold relay R345 in the trunk circuit 300 restores to interrupt, at the contacts 345, the previously mentioned path for applying ground potential to the control conductor C314 of the trunk 310, the previously traced holding circuits for maintaining operated the timer relay R315 and the time release relay 365 in the trunk circuit 300 are interrupted causing these relays to restore. Also, in this connection it is noted that the previously traced holding circuit for energizing the upper winding of the select relay R160 is arranged in multiple with the holding circuit for energizing the winding of the switch relay R in the selector S100, whereby the select relay R restores incident to the restoration of the switch relay R150. When the selector S100 is thus released the line switch 16 is restored, marking the subscriber line 15 extending to the subscriber substation T11 in the central cnice 10 as idle to the connectors in the group, including the connector 19D, having access thereto.

Trunk calls from the central olice 10 to the remote exchange 30 and calls to the Operator switchboard 280 inthe central office 10 At the outset it is noted that the subscriber substations rendered restricted service, such, for

example, as the subscriber substation T| in the central oiiice I0, are not permitted to extend connections to the remote exchange 30 and, specically, that such stations to not have facility for controlling operation of the hunt switches in the secondary trunks 200, etc. in order to bring about this result, as explained more fully hereinafter in conjunction with the extension of connections from subscriber substations rendered non-restricted service and subscriber substations rendered limited service in the centr-al oiice I0. Specifically, a subscriber substation rendered restricted service, such, for example, as the subscriber substation TIS in the central oflice I0, must rst extend a connection to the operator switchboard 280 in the central oice I0, in a manner more fully explained hereinafter, and permit the operator at the switchboard 280 to complete the connection to a called subscriber substation in the remote exchange 30.

Considering now the extension of a call from a subscriber substation rendered non-restricted service, such, for example, as the subscriber substation TI2 in the central oiiice I0 to a called subscriber substation, such for example, as the called subscriber substation T3| in the remote exchange 30, the subscriber at the calling subscriber substation T|2 first initiates the call in order to control the line switch I8 over the associated subscriber line I1, whereby the line switch I8 selects a trunk extending to an idle selector, such, for example, as the trunk |00 extending to the selector SIM. The subscriber at the calling subscriber substation T|2 then dials the rst digit 9 of the directory number of the called subscriber substation TSI in the remote exchange 30. The selector S|00 responds t-o the digit 9 in a manner substantially identical to that previously explained, whereby the Strowger mechanism I 80 iirst selects the group of trunks, including the trunk 2|0, and then an idle trunk therein. Assuming that the selector S|00 selects the trunk 2|0 extending to the s-econdary trunk 200, the trunk 2I0 is marked las idle to the selector S|00 by the application of battery potential to the control conductor C2|3 thereof. The path for applying battery potential to the control conductor C213 of the trunk 2|0 includes the rotary magnet M216 of the hunt switch 210 incorporated in the secondary trunk 200, the contacts 211, the wiper 214 and the engaged home contact in the associated contact bank, and the upper winding of the transfer relay R240. When the selector S|00 has operated, in the manner previously explained, to select the trunk 2|0, ground potential is applied in the selector S|00 to the control conductor C2 I3 of the trunk 2|0, thereby to complete a circuit substantially identical to that traced above for energizing the upper winding of the transfer relay R240 in series with the rotary magnet M216 in the secondary trunk 200, whereby the transfer relay R240 operates. However, the rotary magnet M210 does not operate due to the high series resistance of the upper winding or the transfer relay R240. Also, when the selector' S|00 operated to select the trunk 2|0, in the manner previously explained, a loop circuit is completed between the calling subscriber substation T I2 and the line relay R220 in the secondary trunk 200, which loop circuit extends from ground by way of the lower winding of the line relay R220 and the contacts 253 to the line conductor C2|2 of the trunk 2|0, and from battery by way of the upper winding of the line relay R220 and the contacts 25| to the line conductor C2|l of the trunk 2|0; the line conduc- 22 tors C2|| and C2| 2 of the trunk 2|0 being terminated by contacts in the first section of the contact bank engaged by the line wipers |8|a and |8|b of the first wiper set of the Strowger mechanism in the selector S|00. Accordingly, the line relay R220 in the secondary trunk 200 operates to complete, at the contacts 22|, a path, including the contacts 258, for operating the hold relay R230. Upon operating, the hold relay R230 completes, at the contacts 23|, a multiple circuit for applying ground potential to th-e control conductor C2|3 of the trunk 2|0, thereby to maintain operated the transfer relay R240 in the secondary trunk 200 and the switch relay RI 50 in the selector |00. At this time the secondary trunk 200 is conditioned to respond to the next digit dialed at the calling subscriber substation TI2. The subscriber at the calling subscriber substation T|2 then dials the second digit Y of the directory number of the called subscriber substation T3| in the remote exchange 30. It will, of course, be understood that the subscriber at the calling subscriber substation T|2 merely operates the dial thereat, utilizing the eleventh digit linger hole therein, whereby the dial mentioned causes twelve impulses in a group to be transmitted therefrom over the subscriber line I1, the line switch I8, the trunk |00, the selector S|00, and the trunk 2 I0 to the line relay R220 in the secondary trunk 200, whereby the latter relay follows.

Each time the line relay R220 restores and then reoperates it interrupts and then recompletes, at the contacts 22|, the previously traced circuit for maintaining operated the hold relay R230, whereby the latter relay being of the slowto-release type is maintained operated during impulsing. Also, each time the line relay R220 restores and then reoperates it completes and then interrupts, at the contacts 222, a circuit, including the contacts 258, 233 and 243, for energizing the lower winding of the transfer relay R240, thereby to maintain the latter relay in its operated `position during the reception of the present digit and after the wiper 214 of the hunt switch 210 disengages the home contact in the associated contact bank, interrupting the previously traced circuit for. energizing the upper winding of the transfer relay R240 in series with the rotary magnet M215. Further, each time the line relay R220 restores and then reoperates it completes and then interrupts, at the contacts 222, a multiple circuit, including the contacts 258, 233, 243 and 2li-i, for operating the rotary magnet M216 of the hunt switch 210. Accordingly, in the present example, the line relay R220 receives the twelve impulses of the second digit Y, repeating them, at the contacts. 222, to the rotary magnet M215, whereby the wipers noted of the hunt switch 210 are driven twelve steps in the clockwise direction away from their home positions. When the wipers 21|, 212 and 213 of the hunt switch 210 are thus operated, they are driven across the group of nine trunks, including the trunk 28|, extending to the operator switchboard 280 and into the grou-p of fourteen trunk lines, including the trunk line 280, extending between the central office I0 and the remoteexchange 30. At the conclusion of the second digit Y the line relay R220 isI maintained in its operated position, thereby to interrupt, at the contacts 222, the above-traced circuit for energizing the lower winding of the hold relay R240; and when the wiper 214 of the hunt switch 210 is driven one step in the clockwise direction away from its home position to disengage the home contact in the associated contact bank, it interrupts the previously traced circuit for energizing the upper winding of the transfer relay R24!) in series. with the rotary magnet M216; accordingly the transfer relay R246 restores shortly following the conclusion of the second digit Y.

Upon restoring, the transfer relay R260 completes, at the contacts 242 and 24|, a path, including the contacts 232 and 255, for applying ground potential by way of the winding of the test relay R258 to the wiper 213 of the hunt switch 218, in order to test the idle or busy condition of the trunk line, extending between the central office lil and the remote exchange 30, that is selected by the wipers 21|, 212 and 213 of the hunt switch 215 at this time. In the event the trunk line selected by the wipers 21|, 212 and 213 of the hunt switch 21|] is busy at this time, ground potential is applied to the control conductor thereof in the associated trunk circuit, thereby to complete a path, substantially identical to that previously traced and including the wiper 213 of the hunt switch 210, for shortcircuiting the winding of the test relay R252. On the other hand, in the event the trunk line mentioned is idle at this time, battery potential applied to the control conductor thereof in the associated trunk circuit, and, consequently, to the wiper 213 of the hunt switch 210, completes a circuit substantially identical to that previously traced for energizing the winding of the test relay R259 in order to cause the latter relay to operate. First assuming that the trunk mentioned is busy at thisl time, the ground potential upon the control conductor thereof and applied to the wiper 213 or" the hunt switch 212 completes a circuit, including the contacts 24|,

255 and 211, for operating the rotary magnet 1 M216 of the hunt switch 210, whereby the rotary magnet M215 operates to drive the wipers noted of the hunt switch 219 an additional step in the clockwise direction and to interrupt, at the contacts 211, the operating circuit therefor. Accordingly, the rotary magnet M215 operates buzzer fashion to drive the wipers noted of the hunt switch 210 step by step in the clockwise direction until an idle trunk extending between the central office i6 and the remote exchange 3G is c selected by the wipers 21|, 212 and 213 thereof, whereupon the test relay R258 operates; as previously explained. Now assuming that the trunk line 28S, extending between the central cnice l!) and the remote exchange 3D, is the first idle trunk line in the associated group, when the wipers 21E, 212 and 213 engage the contacts in the associated contact bank terminating the trunk line 285, the test relay R255 operates, as noted above, to complete, at the contacts 251, a holding circuit, including the contacts 23| and 211, for energizing the winding of the test relay R250 in series with the rotary magnet M216, whereby the test relay R255 is retained in its operated position but the rotary magnet M216 is not reoperated, by virtue of the high series resistance of the winding of the test relay R259. Also, the test relay R258 interrupts, at the contacts 255, the previously traced original operating circuit therefor; and completes, at the contacts 25S, a path, including the contacts 23|, for applying ground potential to the wiper 213 of the hunt switch 216 and, consequently, to the control conductor of the trunk line 286; whereby the trunk circuit 281 associated with the trunk line 286 operates in order to return ground potential upon the control conductor of the trunk line 235, whereupon the test relay R250 is maintained in its operated position by virtue of the completed holding circuit for energizing the winding thereof in series with the rotary magnet M215. Also, the test relay R25!) interrupts, at the contacts 25| and 253, the previously traced original loop circuit, extending between the calling subscriber substation T|2 in the central office and the line relay R225 in the secondary trun.; 282; and completes, at the contacts 252 and 254, an alternative loop circuit, extending between the calling subscriber substation T|2 in the central ofce |5 and the trunk circuit 252-1 terminating the trunk line 285 eX- tending between the central oice |0 and the remote exchange 3o. The loop circuit mentioned includes the line wipers 21| and 212 of the hunt switch 21o and the engaged contacts in the associated contact banks. The trunk circuit 28'1 then operates in order to eiect seizure of the switching apparatus 285 in the remote exchange 32 over the trunk line 288. Further, the test relay R255! interrupts, at the contacts 258, the previously traced circuit for maintaining operated the hold relay R230, thereby to cause the latter relay to restore shortly thereafter, it being of the slow-torelease type. Upon restoring, the hold relay R230 interrupts, at the contacts 23|, the original path for applying ground potential to the control conductor C2|3 of the trunk ZEG. However, ground potential is applied to the control conductor C2|3 of the trunk 2|!) from the trunk circuit 231 terminating the trunk line 235i at this time, by virtue of the connection oi the control conductor C2|3 by way of the contacts 258 and the wiper 213 of the hunt switch 21S and the engaged contact in the associated contact bank to the control conductor of the trunk line 285. Accordingly, the test relay R250 in the secondary trunk 22E! as well as the switch relay R in the selector SIGG are maintained in their operated positions, in order to maintain operated the secondary trunk 200 and the selector S I G8 respectively.

At this time the above-traced loop circuit is completed between the calling subscriber substation T|2 in the central cnice Hl and the trunk circuit 281, and the trunk circuit 281 has brought about seizure of the switching apparatusl 285 in the remote exchange S over the trunk line 286, whereby the switching apparatus 285 is conditioned to respond to the third and remaining digits of the directory number of the called subscriber substation TSI in the remote exchange 3c. The subscriber at the calling subscriber substation T|2 in the central oiiice I0 then proceeds to dial the remaining digits of the directory number of the called subscriber substation Ti in the remote exchange 30, which digits are transmitted over the loop circuit extending from the calling subscriber substation T|2 to the trunk circuit 281 and are repeated by the trunk circuit 281 over the trunk line 286 to the switching apparatus 285, in order to cause the switching apparatus 285 to operate and select the subscriber line 28B extending to the called subscriber substation Tl in the remote exchange 3|). The subsequent operation of the switching apparatus 285 depends upon the idle or busy condition of the called subscriber substation TSI at this time; and assuming that the called subscriber substation T3! is idle, when the call is answered thereat, the switching apparatus 285 operates in 0r- 25 der to complete a connection thereto, whereby a connection is established between the calling .subscriber substation T|2 in the central ofiice Il) and the called subscriber substation TSI in the remote exchange 30.

At the conclusion of the connection when the subscriber at the calling subscriber substation TI2 in the central oiiice l0 replaces the receiver of the telephone instrument thereat upon its associated switchhook, the previously traced loop circuit extending therefrom by Way of the selector SIIJI) and the secondary trunk 222 to the trunk circuit 281 is interrupted, in order to cause the trunk circuit 281 to eifect the release of the switching apparatus 285, whereby the subscriber line 288 extending to the called subscriber substation TSI in the remote exchange 3B is marked as idle, assuming that the subscriber at the called subscriber substation TBI has replaced the receiver of the telephone instrument thereat upon its associated switchhook at this time. Also, the trunk circuit 281 operates to interrupt the application of ground potential upon the control conductor of the trunk line 226 and to re-apply battery potential thereto, in order to mark the trunk line 285 as idle to the hunt switches in the secondary trunks 29D, etc. Also, when ground potential is removed from the control conductor of the trunk line 282, the previously traced holding circuit for maintaining operated the test relay R2 5I! in the secondary trunk 200 and the multiple holding circuit for maintaining operated the switch relay Rl in the selector SIGO are interrupted. The switch relay RIE!! restores, effecting the release of the selector Slii in the manner previously explained, whereby the line switch I8 is restored, marking the subscriber line I1 extending to the subscriber substation T|2 in the central omce IE! as idle to the connectors in the group, including the connector ISE), having access thereto.

Upon restoring, the test relay R250 in the secondary trunk 202 completes, at the contacts 259, a path, including the contacts 2313, for applying ground potential to the multiple connected contacts in the contact bank associated with the wiper 214 of the hunt switch 21B, thereby to complete a circuit, including the contacts 211, for operating the rotary magnet M215. The rotary magnet M216 operates. intermittently in order to drive the wipers noted of the hunt switch 212 step by step in the clockwise direction back into their home positions, whereupon the wiper 21- disengages the last multiple grounded contact in the associated contact bank in order to interrupt the above-traced circuit for operating intermittently the rotary magnet M215. When the wiper 214 of the hunt switch 21@ rei-engages the home contact in the associated contact bank, the previously traced path for applying battery potential by way of the rotary magnet M216 and the upper winding of the trans-fer relay R242 to the control conductor C213 of the trunk 2li] is recompleted, thereby again to mark the trunk 2li! and, consequently, the secondary trunk 252, as idle to the selectors Smil, etc. having access thereto. At this time the secondary trunk 292 is completely released and available vfor further use.

Reconsidering the operation of the hunt switch 212i incorporated in the secondary trunk 22B, following the conclusion of the second digit Y ldialed at the calling subscriber substation TI2,

it is noted that the rotary magnet M216 cooperates with the test relay R250 in order to test the trunk lines in the group of fourteen extending between the central cnice lil and the remote exchange 3i), and including the trunk line 286, in the manner previously explained. However, should it occur that all of the trunk lines extending between the central office I0 and the remote exchange 30 are busy at this time, the wipers 21|, 212 and 212 disengage the last contacts in the associated contact bank terminating the last trunk line in the group of fourteen mentioned, and re-engage the home contacts in the associated contact bank. When the wiper 214 of the hunt switch 210 re-engages the home contact in the associated contact bank, the previously traced circuit for energizing the upper winding of the transfer relay R22!! in series with the rotary magnet M216 is recompleted, thereby to cause the transfer relay R24!) to reoperate and interrupt, at the contacts 24| and 222, the previously traced path, including the winding of the test relay R250, for testing over the wiper 213 of the hunt switch 21E! the trunk lines in the group, including the trunk line 286, extending between the central oflice iii and the remote exchange 30. Accordingly, in this peculiar event the secondary trunk 2GB responded to the second digit Y dialed at the calling subscriber substation T|2 in the central oice In, tested the trunk lines extending between the central office IB and the remote exchange 30, and, finding them busy, returned to its original condition, whereby the secondary trunk 22|! failed to switch through and is thus in condition to receive the third digit dialed at the calling subscriber substation TI2. Hence, when the subscriber at the calling subscriber substation TI2 in the central ofhce IB dials the third digit of the .directory number of the called subscriber substation T3| in the remote exchange 30, the third digit mentioned is transmitted tothe line relay R229 in the secondary trunk 22! instead of to the trunk circuit 281, etc. in the usual case. Thus, the line relay R222 responds to the third digit of the directory number of the called subscriber substation T3| in the remote exchange 30, which third digit comprises some digit between 1 and O and brings about corresponding operation of the hunt switch 21E. Accordingly, at the conclusion of the third digit mentioned, when the transfer relay R226 restores, the hunt switch 21u occupies an operated position whereby the wipers 21|, 212 and 213 thereof are disposed in the group of nine trunks, including the trunk 28|, extending to the operator switchboard 289 or engaging the tenth contacts in the associated contact bank terminating no conductors in the special event that the third digit of the directory number of the called subscriber substation TSI in the remote exchange 3|] happened to be 0.

First assuming that the third digit of the directory number of the called subscriber substation T3| in the remote exchange 3B was some digit smaller than 0, such, for example, as the digit 5, the wipers 21|, 212 and 213 ofthe hunt switch 21B engage the fifth contacts in the associated contact banks at the conclusion of the third digit mentioned and when the transfer relay R'fili restores, whereby the nfth trunk extending to the operator switchboard 28o is tested by the secondary trunk 202. At this time the -rotary magnet M212 cooperates with the test relay R252, in the manner previously explained, in order to cause the fth and following trunks in the group extending to the operator switchboard 286 to be tested, in the manner previously tor switchboard 280.

27 explained. In the event one of the trunks mentioned is idle, the hunt switch 210 selects Athis idle trunk, thereby extending the connection thereover to the koperator switchboard 280 inci- -den to Voperation of the test relay R250. However, in the event the fth and following trunks extending to the operator switchboard 280 are busy, the wipers noted of the hunt switch 210 are driven to engage the tenth contacts in the vassociated `contact banks. in the contact banks associated with the wipers 21|, 212 and 213 of the hunt switch 210 engage no conductors. However, 'the wiper 215 oi the hunt switch '210 engages the grounded tenth contact in the associated contact bank, thereby completing a circuit, including the contacts 253 and 245, for energizing the upper winding of the lockout relay R260 in series with the rotary magnet M216. When this series circuit is completed, the lockout relay R260 operates. ever, the rotary magnet M216 does not operate due to the high series resistance of the upper winding of the lockout relay R260. Upon operating, .the lockout relay R260 completes, at the contacts 262, an obvious holding circuit for energizing the upper and lower windings thereof in series; .and interrupts, at the contacts 263, the previously traced original circuit for energizing .the upper winding 'thereof in series with the rotary magnet M216. Also, the lockout relay R260 completes, at the contacts 264, a path for 'groundingthe eleventh to twenty-fourth and home 'contacts in the contact bank lassociated with the wiper 215 of the hunt switch 210. Finally, the lockout relay R288 completes, at the contacts 26|, a 'direct circuit, including the contacts 211, for operating the rotary magnet M215. The rotary magnet M216 operates intermittently to drive the wipers noted of the hunt switch 210 from engagement with the tenth contacts in the 'associated contact banks through the twenty-fourth and then home positions, and into engagement with Ythe rst contacts in the associated contact "banks terminating the first trunk in the group extending to the -operator switchboard 280. When the hunt switch 210 is driven through `its home position the wiper 215 thereof disengages the grounded home contact in the associated-contact bank, interrupting the previously traced holding circuit for maintaining operated 'the lockout relay R260, whereby the latter relay restores, interrupting, at the contacts 26|, the direct circuit for operating intermittently the rotary magnet M216. Accordingly, at this time the rst and following trunks extending to the operator switchboard 280 .are

tested by the secondary trunk 200. It will be understood that the arrangement including the lockout relay 'R260 vpositively prevents the .hunt 'switch 2:10 from testing the second time any of the trunk lines extending between the central oi'lice vIll and the remote exchange 30.

The hunt .switch 210 operates, in the manner explained above, repeatedly to test the trunks -in the group extending to the operator switchboard 280 and until an idle trunk extending thereto is found. Assuming that the trunk 28|, extending to the operator switchboard 280, is idle at this time, the hunt switch 210 operates to select the trunk 28| and to bring about operation 1of the test relay R250, thereby to complete a connection between the calling subscriber substation T|2 in the central oflice I0 and the opera- At this ltime the trunk circuit 282 associated with the trunk 28| operates to mark the trunk 28| as busy to the hunt The tenth contacts y How- -v switches of the other secondary trunks having access thereto. The operator at the switchboard 280 then answers the call, completing a connection to the calling subscriber substation T|2 in the central office IU, advising the subscriber thereat that the present call was intercepted by virtue of the all-busy condition of the trunk lines extending between the central office |0 and the remote exchange 30. The release of the established connection between the calling subscriber substation T|2 and the operator switchboard 280 is the same as the previously described connection and is brought about in response to the release operation performed at the calling subscriber substation Tl2, whereby the loop circuit extending to the trunk circuit 282 is interrupted, causing the trunk circuit 282 to operate, interrupting the application of ground potential to the control conductor of the trunk 28| and returning battery potential thereto, whereby the trunk 28| is marked as idle to the hunt switches of the secondary trunks having access thereto, assuming that the operator at the switchboard 280 has disconnected from the trunk 28| at this time The release of the secondary trunk 20e and the selector SIU!) then takes place, in the manner previously explained.

In the foregoing explanation it was assumed that the third digit of the directory number of the called subscriber substation TSI was other 'than 0 and was, in fact, 5. However, inthe event the third digit of the directory number of the called subscriber substation T3| in the remote exchange 30 had been 0, the operation of the secondary trunk 200 would have been substantially 'the same as that described above except that 'the lockout relay R260 would have operated immediately followingr `the restoration of the transfer relay R240 at the conclusion -of the third digit mentioned. At this point it is noted that the operation of the secondary trunk 260 as described above, when all of the trunks extending between the central office I0 and the remote exchange 32 are tested as busy, and when the third digit of the directory number of the called subscriber substation T3| in the remote exchange 30 is 0, is precisely the same as that of the secondary trunk 200 when the second digit dialed at the calling subscriber substation T|2 is '0, which second digit 0 in conjunction with the first digit 9 comprises the directory number of the operator switchboard 280.

In view of the above it will be appreciated that when a call is initiated at the calling subscriber substation T|2 rendered non-restricted service in the central ofiice I0, that is to be extended to the operator switch 280 therein, the subscriber at the lcalling subscriber substation T|2 dials the twodigits 9 and O in order to bring about operation viirst of the selector Sl, etc. and then of the secondary trunk 200, etc. in the manner explained immediately above, in order to route the call to the operator switchboard 280. In this connection it will be appreciated that the lockout relay R250 in the secondary trunk 200, for example, operates immediately following the second digit 0 when the transfer relay R240 restores, -in order to initiate operation of the hunt switch 210 to search for an idle trunk extending to the operator switchboard 280, in the manner explained above. The release of this established connection between the calling subscriber substation T|2 and the operator switchboard 280 in the central oiiice I0 is the same as that previously described.

Considering now the extension of a call from a subscriber substation rendered limited service, such, for example, as the subscriber substation T|| in the central office l to a called subscriber substation, such, for example, as the called subscriber substation T3| in ythe remote exchange 30, the subscriber' at the calling subscriber substation TH rst initiates the call in order to control the line switch i6 over the associated subscriber line l5, whereby the line switch I6 selects a trunk extending to an idle selector, such, for example, as the trunk M30 extending to the selector S102.' The subscriber at the calling subscriber substation TH then dials the first digit 9 of the directory number of the called subscriber substation T3! in the remote exchange 36. The selector Slet responds to the digit 9 in the manner previously explained, whereby the Strowger mechanism |82 iirst selects the group of trunks, including the trunk 2HE, and then an idle trunk therein. Assuming that the selector SID@ selects the trunk 2H) extending to the secondary trunk 260, the trunk 215; is marked as idle to the selector S|00 by the application of battery potential to the control conductor C2|3 thereof. The path for applying battery potential to the control conductor C213 of the trunk 2li! includes the rotary magnet M215 of the hunt switch 210 incorporated in the secondary trunk 220, the contacts 211, the wiper 212 and the engaged home contact in the associated contact bank, and the upper winding of the transfer relay R242. When the selector SIDO has operated, in the manner previously explained, to select the trunk 2 i 6, ground potential is applied in the selector Slet! to the control conductor C2i3 of the trunk 2 El, thereby to complete a circuit substantially identical to that traced above for energizing the upper winding o1 the transfer relay R242 in series with the rotary magnet M216 in the secondary trunk 202, whereby the transfer relay R220 operates. However, the rotary magnet M216 does not operate due to the high series resistance of the upper winding of the transfer relay R242. Also, when the selector Siti) operated to select the trunk 2li?, in the manner previously explained, a loop circuit is completed between the calling subscriber substation T|| and the line relay R229 in the secondary trunk 200, which loop circuit extends from ground by way of the lower winding of the line relay R226 and the contacts 253 to the line conductor C2|2 of the trunk 2li), and from battery by way of the upper winding of the line relay R225 and the contacts 25| to the line conductor C2| I of the trunk 2 lil; the line conductors C2i I and C2H2 or" the trunk 2 i E! being terminated .by contacts in the iirst section of the contact bank engaged by the line Wipers |8|a .and |8|b of the iirst wiper set of the Strowger mechanism |80 in the selector SIM). Accordingly, the line relay R225 in the secondary trunk 229 operates to complete, at the contacts 22|, a path, including the contacts 258, for operating the hold relay R232. Upon operating, the hold relay R230 completes, at the contacts 23|, a multiple circuit for applying ground potential to the control conductor C2|3 of the trunk 2li), thereby to maintain operated the transfer relay R222 in the secondary trunk 22e and the switch relay RiE in the selector |62. At this time the secondary trunk 200 is conditioned to respond to the next digit dialed at fthe calling subscriber substation T||. The subscriber at the calling subscriber substation Tl! then dials the second digit X of the directory number of the called subscriber substation TBI in the remote exchange 30. It

will, of course, be understood that the subscriber at the calling subscriber substation TH merely operates the dial thereat, utilizing the eleventh digit finger hole therein, whereby the dial mentioned causes eleven impulses in a group to be transmitted therefrom over the subscriber line l5, the line switch i6, the trunk |22, the selector SISB, and the trunk 2| Q to the line relay R226 in the secondary trunk 200, whereby the latter relay follows.

Each time the line relay R220 restores and then reoperates it interrupts and then recompletes, at the contacts 22|, the previously traced circuit for maintaining operated the hold relay R230, whereby the latter relay being of the slowto-release type is maintained operated during impulsing. Also, each time the line relay R220 restores and then reoperates it completes and then interrupts, at the contacts 222, a circuit, including the contacts '258, 233 and 243, for energizing the lower winding of the transfer relay R240, thereby to maintain the latter relay in its operated position during the reception of the present digit and after the wiper 212 of the hunt switch 210 disengages the home contact in the associated contact bank, interrupting the previously traced circuit for energizing' the upper vwinding of the transfer relay R246 in series with the rotary magnet M216. Further, each time the line relay R226 restores and then reoperates it completes and then interrupts, at the contacts 222, a multiple circuit, including the contacts 258, 233, I2113 and 244, for operating the rotary magnet M216 of the hunt switch 210. Accordingly, in the present example, the line relay R220 receives the eleven impulses of the second digit X, repeating them, at the contacts 222, to the rotary magnet M216, whereby the wipers noted of the hunt switch 210 are driven eleven steps in the clockwise direction away from their home positions. When the wipers 21|, 212 and 213 of the hunt switch 210 are thus operated, they are driven across the group of nine trunks, including the trunk 28|, extending to the operator switchboard 280 and into the group of fourteen trunk lines, including the trunk line 286, extending between the central oiiice l0 and the remote exchange 30. At the conclusion of the second digit X the line relay R220 is maintained in its operated position, thereby to interrupt, at the contacts 222, the above-traced circuit for energizing the lower winding of the hold relay R240; and when the wiper '214 of the hunt switch 210 is driven one step in the clockwise direction away from its home position to disengage the home contact in the associated contact bank, it interrupts the previously traced circuit for energizing the upper winding of the transfer relay R240 in series with the rotary magnet M216; accordingly the transfer relay R240 restores shortly following the conclusion of the second digit X.

The operation of the hunt switch 210 to test the trunk lines extending between the central oiiice I0 and the remote exchange 30 at the conclusion of the second digit X is the same as that previously explained, whereby the hunt switch 210 operates to select a trunk line in this group, in the event one of these trunk lines is idle at this time. The subscriber at the calling subscriber substation T|| in the central office if! then proceeds to dial the third and remaining digits of the directory number of the called subscriber substation T3| in the remote exchange 30, in order to bring about the completion of an established connection therebetween, in the manner previously explained. The release of this established connection between the calling subscriber substation Tl I in the central office I and the called subscriber substation T31 in the remote exchange 3i) is under the control of the subscriber at the calling subscriber substation TH and is brought about when the receiver of the telephone instrument thereat is returned to its associated switchhook, as previously explained.

It is again noted that in the event all of the trunk lines extending between the central oiice I0 and the remote exchange 30 are busy at the conclusion of the second digit X, the hunt switch 2li), after testing all of the trunk lines mentioned, is returned to its home position. Subsequently, the hunt switch 210 responds to the third digit of the directory number of the called subscriber substation TSI in the remote exchange 30 that is dialed at the calling subscriber substation 'III in the central oice i0, in order to bring about operation thereof to extend the connection to the operator switchboard 23B-, all in the manner previously explained.

Also, in view of the prior explanation of the extension of a connection from the calling subscriber substation Ti2 to the operator switchboard 280 in the central oflce i9, it will be understood that a connection may be extended in an identical manner from the calling subscriber substation Tll to the operator switchboard 280 in the central office I0; the subscriber at the calling subscriber substation TII dialing the digits 9 and 0 comprising the directory number of the operator switchboard 280.

In View of the foregoing description of the extension of connections from the calling subscriber substations T42 and TI l, respectively rendered non-restricted service and limited service, to the operator switchboard 280 in the central office l0, it will be understood that a call from a subscriber substation rendered restricted service, such, for example, as the subscriber substation T10, to the operator switchboard 28!! in the central ofce i0 may be extended in an identical manner; the subscriber at the calling subscriber substation TIG dialing the two digits 9 and 0. Also, the subsequent release of this connection between the calling subscriber substation Tl 8 and the operator switchboard E30 in the central ofhce EB is the same as that previously described.

In the telephone system the arrangement including the selector SUIS and the line trunk circuit 399 is disclosed and claimed in the previously mentioned Wicks application.

there has been provided an automatic telephone system comprising subscriber substations rendered three diilerent classes of service characterized by three dierent types of dialing apparatus at the respective classes of subscriber substations, and automatic switching apparatus selectively controllable in accordance with the types of dialing apparatus at the calling subscriber substations connected thereto, in order to render the three different classes of service mentioned.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may bo made therein, and it is in tended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a telephone system including subscriber substations of first and second classes, automatic switching apparatus accessible to said subscriber substations, an operator switchboard, a rst group of trunks extending to said operator switchboard, and a second group of trunks extending to a remote point; said switching apparatus including a contact bank provided with rst and second sections and a cooperating wiper having a home position and operable away from its home position successively over said first and second sections of said contact bank, said rst and second groups of trunks being respectively terminated in said first and second sections of said contact bank, each of said subscriber substations of said second class being provided with a conventional digit transmitting mechanism and each of said subscriber substations of said first class being provided with a unique digit transmitting mechanism capable of a special operation to transmit a special control, means responsive to a given digit for operating said wiper to Search for an idle trunk in said rst section of said contact bank, means responsive to said special control for operating said Wiper to search for an idle trunk in said second section of said contact bank, and means for preventing said wiper from searching over said rst section of said contact bank into said second section of said contact bank.

2. In a telephone system including subscriber substations of rst and second classes, automatic switching apparatus accessible to said subscriber substations, an operator switchboard, a rst group of trunks extending to said operator switchboard, and a second group of trunks extending to a remote point; said switching apparatus including a contact bank provided with iirst and second sections and a cooperating wiper having a home position and operable away from its home position successively over said irst and second sections of said contact bank, said first and second groups of trunks being respectively terminated in said first and second sections of said contact bank, each of said subscriber substations of said second class being provided with a conventional digit transmitting mechanism and each of said subscriber substations of said first class being provided with a unique digit transmitting mechanism capable of a special operation to transmit a special control, means responsive to a given digit for operating said wiper to search for an idle trunk in said first section of said contact bank. means responsive to said special control for operating said wiper to search for an idle trunk in said second section of said contact bank, and means for causing said wiper to Search repeatedly said first section of said contact bank if necessary and for preventing it from searching over said first section of said Contact bank into said second section of said contact bank.

3. In a telephone system including subscriber substations of first and second classes, automatic switching apparatus accessible to said subscriber substations, an operator switchboard, a first group of trunks extending to said operator switchboard. and a second group of trunks extending to a remote point; said switching apparatus including a contact bank provided with first and second sections and a cooperating wiper having a home position and operable away from its home position successively over said rst and second sections of said contact bank, said iirst and second groups of trunks being respectively terminated in said first and second sections of said contact bank,

each of said subscriber substations of said second class being provided with a conventional digit transmitting mechanism and each of said subscriber substations of said first class being provided with a unique digit transmitting mechanism capable of a special operation to transmit a special control, means responsive to a given digit for operating said Wiper to search for an idle trunk in said rst section of said contact bank, means responsive to said special control for operating said Wiper to search for an idle trunk in said second section of said contact bank, and means controlled by said Wiper searching over said second section of said contact bank for causing it to search into said rst section of said contact bank and for preventing it from searching over said iirst section of said contact bank again into said second section of said contact bank.

4. In a telephone system including subscriber substations of iirst and second classes, automatic switching apparatus accessible to said subscriber substations, an operator switchboard, a rst group of trunks extending to said operator switchboard, and a second group of trunks extending to a remote point; said switching apparatus including a Contact bank provided with first and second sections and a cooperating wiper having a home position and operable away from its home position successively over said rst and second sections of said contact bank, said first and second groups of trunks being respectively terminated in said rst and second sections of said contact bank, each of said subscriber substations of said second class being provided with a conventional digit transmitting mechanism and each of said subscriber substations of said rst class being provided with a unique digit transmitting mechanism capable of a special operation to transmit a special control, means responsive to said special control for operating said Wiper to search for an idle trunk in said second section of said contact bank, means responsive jointly to failure of said wiper to iind an idle trunk in said second section of said contact bank and to a subsequent digit for operating said wiper to search for an idle trunk in said iirst section of said contact bank, and means for preventing said Wiper from searching over said rst section of said contact bank again into said second section of said contact bank.

5. In a telephone system including subscriber substations of first and second classes, automatic switching apparatus accessible to said subscriber substations, an operator switchboard, a rst group of trunks extending to said operator switchboard, and a second group of trunks extending to a remote point; said switching apparatus including a contact bank provided with first and second sections and a cooperating wiper having a home position and operable away from its home position successively over said rst and second sections of said contact bank, said first and second groups of trunks being respectively terminated in said rst and second sections of said contact bank, each of said subscriber substations of said second class being provided with a conventional digit transmitting mechanism and each of said subscriber substations of said rst class being provided with a unique digit transmitting mechanism capable of a special operation to transmit a special digit that is greater than 0, means responsive to the digit 0 for operating said wiper to search for an idle trunk in said rst section of said contact bank, means responsive to said special digit for operating said wiper to search for an idle trunk in said second section of said contact bank, and means for preventing said wiper from searching over said first section of said contact bank into said second section of said contact bank.

JOHN WICKS.

REFERENCES CITED UNITED STATES PATENTS Name Date Olson Jan. 23, 1934 Number 

